Rjust on Ironweed

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cottelpg Hamilton, OH(Zone 6a) Aug 10, 2014

I posted this on another forum and did not get a response. I hope someone here will have a suggestion.

When I returned from vacation my Vernonia gigantea was riddled with rust. I have grown this plant for years and have never encountered this before. Does anyone have a suggestion on how I can prevent this in the future? This was very disappointing as I rely on my Ironweeds for late summer color.




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Diana_K Contra Costa County, CA(Zone 9b) Aug 16, 2014

Preventative sprays.
Rusts are fungi that are often host specific, at least to the plants' family level. So the rust on Veronia may not be the same species as might be found on Hollyhock, or roses for example. I wonder if the one on your Veronia is the same as any of 3 that are known to infest Aster?

The control is essentially the same, though. Get anti-fungal materials on the plant before the rust. Then, when the rust spores germinate they will not be successful.
Make sure you get the underside of the leaf, as well as the top.

You can try cleaning up some of the overwintering spores with sprays in the fall and spring. Then continue spraying (timing will depend on the product) as long as the weather favors rust.

http://extension.umass.edu/floriculture/fact-sheets/rust-diseases-ornamental-crops

Post #9919438
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cottelpg Hamilton, OH(Zone 6a) Aug 18, 2014

Thank you so much for your insight Diana_K. I also found the article quite informative.

My ironweed is Vernonia gigantea. I am unsure as to whether it is among the three you mentioned in your reply.


Do you think Neem oil spray would be effective against rust? I have successfully controlled powdery mildew and black spot with Neem.

Post #9920760
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Diana_K Contra Costa County, CA(Zone 9b) Aug 18, 2014

It is worth a shot. From what I can find out it is effective on some rusts, but not on the most common rust on roses. Since your plant is closer related to Aster, I am making the assumption that the rust is the one most common in that family.

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DonnaMack Elgin, IL(Zone 5a) Aug 25, 2014

I absolutely agree with Diana's advice. I didn't see the question on another forum, but this answer is great, and worth the wait.

I have 30 roses and never have problems with disease because of a preventative program of All Season oil and sulphur, as well as removal of debris. And when the humidity goes up, but the temps stay below 80 (to avoid burning the foliage) I give them another shot of sulphur. I try to keep it to once a month. I use Bonide's sulphur concentrate, since it is so much less expensive to buy a concentrate and my own spray bottle and dilute and spray.

It's not often that you see all of the methods in one place. Very cool.

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